The present invention relates to a rotation transmitting mechanism and an optical scanning probe that uses the rotation transmitting mechanism.
Obtaining a cross-sectional image of a sample under measurement such as biological tissue without cutting thereinto may be achieved using a method of optical coherence tomography (OCT) measurement. OCT measurement is a kind of optical interferometric measurement using the optical interference that occurs only when the optical path lengths of the measuring light and the reference light, into which the light from the light source is divided, are matched to within the coherence length of the light from the light source.
An optical tomographic imaging device that obtains a tomographic image using OCT measurement employs an optical scanning probe that is inserted into the test body so as to scan the sample using measuring light. This OCT optical scanning probe comprises, for example, a mechanism that rotates a flexible shaft so as to rotate a lens, mirror, and optical fiber that are fixed to the flexible shaft via a connecting member, and obtains information on the tomographic image in a body when inserted into a forceps channel of an endoscope and made to perform a lateral scan in the test body.
The flexible shaft is a hollow member having flexibility, and the flexible shaft employed generally comprises a two-layered (dual) coil spring with each layer coil wound in a different direction (Refer to JP06-205775A and JP06-090954A). However, with a two-layered coil spring, the rotation followability at the tip is insufficient, sometimes causing an increase in the rotational speed variation of the lens and other components disposed at the tip section of the probe. Further, the two-layered coil spring has rotational torque transmissibility in one direction only, resulting in a significant decrease in torque transmissibility during rotation in the other direction. Conversely, in JP2001-079007A is proposed a design wherein the coil spring is provided with a triple winding so that the rotation and movement operations are transmitted with good followability to the tip area of the flexible shaft.
Nevertheless, the inventors of the present invention found that, even with a three-layered coil spring, torque transmissibility is optimally exhibited in one rotational direction, but tends to decrease during rotation in the opposite direction. This is because rotation in the direction opposite the winding direction of the outermost layer coil of the coil spring is considered to be in a direction in which the winding of the outermost layer coil loosens, causing an increase in the diameter of the outermost layer coil and, in turn, contact with the inner surface of the probe sheath, thereby hindering smooth rotation of the flexible shaft. Further, when the outermost layer coil contacts the sheath inner surface, the possibility exists that the sheath inner surface will get scratched. Furthermore, with a conventional two-layered coil spring and three-layered coil spring, the problem arises that, in a case where self-induced vibration caused by rotational vibration occurs, the vibration cannot be suppressed.